This invention relates in general to photodetectors and, in particular, to an improved photodetector and a device employing the photodetector for converting an optical signal into an electrical signal.
CD-ROM and DVD-ROM drives have become increasingly important and popular for use with personal computers and amusement game machines. CD-ROM and DVD-ROM drives typically employ optical pickup usually comprising two tracking photodetectors and four high speed split photodetectors, such as that explained and shown in the article “High Speed SI-OEIC (OPIC) For Optical Pickup,” by Takimoto et al., IEEE Transactions on Consumer Electronics, Vol. 44, No. 1, February 1998, pages 137-142.
As noted by the Takimoto article, CD-ROM and DVD-ROM drives are progressing in terms of system compactness and performance. But when the size of these drives are reduced, cross-talk has become an issue due to the close spacing between the components of the drive. To reduce the influence of external noise from the motor and other electrical circuits, the photodiode used in optical pickup has been integrated with the preamplifier circuit that is used to amplify the output of the photodetector.
CD-ROM and DVD-ROM drives have increasingly been used for reading video data, such as data for motion pictures. For such applications and for improved performance in other applications, it is important for the CD-ROM and DVD-ROM drives to have wide bandwidths.
Optical pickup components currently employed in CD-ROM and DVD-ROM drives are typically bipolar devices. While bipolar devices may have acceptable performance for such applications, with the intense competition in the consumer electronics industry, it is desirable to provide alternative designs that are cheaper than the current optical pickup designs.
None of the above-described conventional optical pickup devices for CD-ROM and DVD-ROM drives are entirely satisfactory. It is, therefore, desirable to provide an improved optical pickup and photodiode design to avoid some of the difficulties described above.